Investigation of the dynamics of the O2/Si(001) adsorption system by small-angle ion-surface scattering

The small non-adiabaticity associated with the slow collision of a 450 eV to 3 keV O 2 + beam incident at 5° to a carefully flattened Si(001) surface was used to probe the adiabatic potential energy surface for the O 2 /Si(001) adsorption/reaction system in the limit of low coverage. The scattering products include O 2 − and O − . From the observation of efficient O 2 − formation and th dependence of the negative-ion yields on beam energy, we infer that O 23 − is an intermediate or precursor in the dissociative chemisorption of O 2 on Si(001). The total yield of negative ions (O 2 − and O − ) is high in comparison with similar experiments on th O 2 /Ag(111) system. This may be explained by a reduced reneutralisation probability on the exit trajectory due to the band gap of Si.